Electric Impedance of Marine Egg Membranes

Abstract

ALTERNATING current impedance measurements were made during the past summer on unfertilized and fertilized Arbacia punctulata eggs to determine whether or not an interpretation which has been given^1,2 for the low-frequency increase of capacity on fertilization is correct. The earlier data on Hipponoë³ (Tripneustes) esculentus and Arbacia¹ egg suspensions showed the presence of two capacity elements, and it was suggested that the plasma membrane capacities of about 0·8 µf./cm.² remained unchanged on fertilization and that the fertilization membranes appeared with capacities of about 2 and 3µf./cm.² respectively. The capacity element of the fertilized egg suspensions which was attributed to the plasma membrane has been much less pronounced in the recent measurements on both suspensions⁴ and single eggs⁵, and it has also been found, for both unfertilized and fertilized eggs, that the relatively non-conducting membrane lies either at or very close to the plasma membrane. Thus the increase in capacity on fertilization is probably due entirely to a change in the plasma membrane. It is possible that the second capacity element shown by the older measurements was due to unfertilized eggs in the fertilized suspensions.